Digital automatic test equipment (ATE) faces a variety of conflicting goals, including tight timing accuracy, low cost, and high channel density. Calibration can affect the performance of such ATE, including timing accuracy.
In ATE, timing accuracy refers to applying signals to a device under test (DUT) that meet predefined timing constraints. For example, the rising edge of a signal may need to reach the DUT within a specified time-frame in order to test the DUT accurately. As the operational speeds of DUTs increase, timing accuracy becomes more critical, since there is typically less tolerance for signal time variations during testing.
The timing accuracy of ATE is dictated by its hardware and by techniques used to calibrate the ATE. For particular ATE, different calibration methods can yield different timing accuracies. Therefore, proper calibration is one way to improve timing accuracy without the often substantial cost of upgrading the ATE's hardware.
Some ATE use an on-board calibration matrix to perform channel-to-channel timing alignment. An example of such a calibration matrix 10 is shown in FIG. 1. Here, measurements made through calibration matrix 10 provide channel-to-channel timing offset information, which can be used to calibrate individual ATE channels. An alternate approach to calibration, which uses external equipment, is shown in FIG. 2. Here, an external oscilloscope 12, together with a probing robot 14, directly measure the timing offset of each ATE channel 16. This information can be used to calibrate individual ATE channels.
The approaches shown in FIGS. 1 and 2 have advantages and disadvantages.